Fluid pump with pressure relief path

Abstract

A liquid pump including a pump housing having an interior sidewall forming an interior. The housing has an inlet port and an outlet port. A liner is disposed in the interior and has opposed transverse openings in line with the inlet and outlet ports. The liner has a central longitudinally extending bore. A pump piston is axially and rotatably slidable within the liner longitudinal bore for pumping the liquid from the inlet port to the outlet port. A seal assembly is secured to the pump housing adjacent to an upper end of the liner. The seal assembly including a seal body, an upper end of the piston extending though the cap and in sealing engagement with the seal body, the seal assembly and liner upper end forming a cavity there between. An upper end of the piston extending though the seal assembly and in sealing engagement with the seal body, the seal body and liner upper end forming a cavity there between. The housing having a passageway providing a fluid communication between the cavity and the inlet port.

What is claimed is: 
     
       1. A liquid pump comprising:
 a pump housing having a sidewall forming an interior, the housing having an inlet port and an outlet port; 
 a liner disposed in the interior and having opposed transverse openings in line with the inlet and outlet ports, the liner having a central longitudinally extending bore; 
 a pump piston axially and rotatably slidable within the liner longitudinally extending bore for pumping a liquid from the inlet port to the outlet port; 
 a seal assembly secured to the pump housing adjacent to an upper end of the liner, the seal assembly including a seal body, and an upper end of the piston extends through and beyond the seal assembly and is in sealing engagement with the seal body, the seal assembly and liner upper end forming a cavity there between; and 
 the housing interior sidewall having a channel forming a passageway providing a fluid communication between the cavity disposed above the liner upper end and the inlet port. 
 
     
     
       2. The liquid pump as defined in  claim 1 , wherein the channel is open to the liner along a length of the channel. 
     
     
       3. The liquid pump as defined in  claim 1 , wherein the housing has a top end, and the passageway extends between the housing top end and the inlet port. 
     
     
       4. The liquid pump as defined in  claim 3 , wherein the liner upper end is disposed below the housing top end defining a space. 
     
     
       5. The liquid pump as defined in  claim 4 , wherein the space contributes to a volume of the cavity. 
     
     
       6. The liquid pump as defined in  claim 1 , wherein the housing has a rim that extends above the liner upper end and a washer engages the housing rim forming a gap between the washer and the liner upper end, the gap forming part of the cavity and being in communication with the passageway. 
     
     
       7. A liquid pump comprising: a pump housing having a sidewall forming a housing interior, and the housing having an inlet port and an outlet port; a liner disposed in the housing interior and having openings in communication with the inlet and outlet ports, the liner having a central axially extending bore; a pump piston axially and rotatably slidable within the liner central bore for pumping the liquid between the inlet and outlet ports; and the piston, housing, and an upper end of the liner defining a cavity therebetween, the housing including a passageway in the housing interior sidewall, the passageway extending in the axial direction along a length of the interior sidewall and providing fluid communication between the cavity disposed above the upper end of the liner and the inlet port. 
     
     
       8. The liquid pump as defined in  claim 7 , wherein the liner is disposed between the piston and the housing. 
     
     
       9. The liquid pump as defined in  claim 8 , wherein the liner upper end is disposed below a housing top end defining a space. 
     
     
       10. The liquid pump as defined in  claim 9 , wherein the space contributes to a volume of the cavity. 
     
     
       11. The liquid pump as defined in  claim 7 , wherein the passageway is a channel formed in a surface of the housing interior sidewall. 
     
     
       12. The liquid pump as defined in  claim 11 , wherein the channel is open to the liner along a length of the channel. 
     
     
       13. The liquid pump as defined in  claim 7 , wherein the passageway is a duct formed within the housing interior sidewall, the duct having an enclosed sidewall extending along a length of the duct and having a first opening in communication with the cavity and an opposed second end in communication with the inlet port. 
     
     
       14. The liquid pump as defined in  claim 7 , further including a seal assembly secured to the pump housing adjacent to the upper end of the liner, the seal assembly including a seal body having a recess for receiving a biasing member for urging a portion of the seal body into sealing engagement with the piston. 
     
     
       15. A method for reducing leakage of the liquid pump as defined in  claim 7 , the method comprising the steps of: creating a negative pressure at the inlet of a pump housing of the pump with a piston axially movable within a liner disposed in a chamber of the pump housing; creating a positive pressure at an outlet of the pump housing with the piston; and transferring liquid from the cavity formed in the pump housing to and from the inlet via the passageway formed in the pump housing extending between the inlet and the cavity. 
     
     
       16. The method as defined in  claim 15 , wherein the pump housing chamber has a sidewall and the passageway includes a duct formed within the sidewall.